Wash you hair thoroughly, twice, with a fairly strong shampoo like vosene. This will strip off any products coating the hair, and allow the conditioner to really penetrate properly.
Rinse off the shampoo with very warm water to open the cuticles on the hair shaft, quickly squeeze (not wring) your hair til it's almost dry, then apply a big fat dollop of a deep conditioning treatment, and comb through with a wide tooth comb or your fingers so it covers all your hair and feels quite wet.
Then pin up your hair and wrap your head in clingfilm, and for an extra step, give it a blast with your hairdryer on a low setting to warm everything up and get it soaking in. When it's all nice and warm, wrap your head in a towel and go and relax somewhere for 20 - 30 min.
Rinse it off thoroughly with warm water, then do a final rinse with cold/cool water to seal the cuticles up again and make it shine. Blowdry around a brush, should be nice and soft and smooth.
Boots do a nice banana hair mask, smells good enough to eat.